Integrated circuits (IC's) comprise a number of semiconductor devices formed on a single substrate or monolithic chip and are finding increased use in electronic circuit applications, because of their small size, low cost and high reliability. They are especially useful for small signal processing circuits. Large numbers of transistors, resistors and diodes, as well as small capacitors, can easily and economically be constructed upon a small "chip" which is typically 2,000 to 10,000 square mils in area. The chip circuitry requires terminal connections for signal coupling and operating potentials. Additionally, inductive circuit elements, large capacitors and other external components are connected to the chip via terminals. Complex integrated circuits generally include a voltage regulator to provide a substantially constant internal source of DC potential for portions of the IC circuitry.
Monolithic technology is a complex subject. However, a brief summary of integrated circuit construction may be helpful. Electronic circuit devices are formed on the wafer, or chip, of semiconductor material, generally silicon, by depositing or implanting regions of N or P semiconductor material in predetermined patterns. N material may be thought of as a source of electrons and P material as a source of positive charges called holes. For example, a diode comprises adjacent deposits of P and N materials. Similarly, a PNP transistor is formed by a sandwich of two regions of P material separated by a region of N material, with the N material defining the base and the P regions the emitter and collector. Selected portions of the circuitry within the chip are connected by conductive paths to bonding pads located near the chip periphery.
The monolithic chip is packaged, or encapsulated, within an insulating container and connections are made, generally by bonding gold filament-like leads, between each of the bonding pads and a corresponding terminal. Once encapsulated, the IC package is an insulated, sealed capsule having a limited number of exposed terminals for making connections between external devices and those within the chip.
The commonly used integrated circuit packages in consumer electronics are of the dual-in-line configuration in which a flat elongated molded capsule houses a monolithic chip and supports two parallel rows of terminals along each side, giving the package a caterpillar-like appearance. Such packages generally have from 12 to 24 terminals. Configurations with more than 24 terminals have disadvantages, such as difficulty of insertion into a mating socket without terminal damage and a much higher probability of defective terminal bonding connections.
IC economics is also largely predicated on high volume production and consequently there is great emphasis placed on standard packaging. Often, desirable circuit changes are not implemented for lack of a terminal. Similarly, a large number of devices may be in use and servicing considerations dictate that succeeding devices be compatible and interchangeable. There may, of course, be any number of situations where an "extra pin" is desired on an IC, or where it is desirable to couple an additional signal to the IC.
In accordance with the invention, a terminal coupled to a voltage regulator in an IC may also be used to couple an external signal to the IC.